What is AVP (arginine vasopressin) and when is it released?

• A. AVP is a diuretic hormone that promotes water loss
• B. AVP is an anti diuretic hormone that promotes water absorption and is released when blood is too concentrated
• C. AVP is a hormone that increases urine production
• D. AVP is produced in the liver and has no effect on kidneys

Answer: (B)

AVP, or arginine vasopressin, is an antidiuretic hormone that promotes water reabsorption in the kidneys. It is released from the posterior pituitary in response to increased plasma osmolality (blood becoming more concentrated) or reduced circulating volume. In the kidneys, AVP binds to V2 receptors on collecting duct cells, triggering the insertion of aquaporin-2 water channels into the apical membrane. This makes the ducts more permeable to water, so more water is reabsorbed back into the bloodstream, resulting in less urine and a more concentrated urine. It is not produced in the liver, and its primary role is to conserve water rather than promote diuresis.